1. Field of the Invention
The present invention relates to an improved method for transmitting and receiving signals having data such as electrical power metering information over power lines. The invention uses a transmission signal such as either a phase modulated, frequency modulated or amplitude modulated signal that is is superimposed onto the transmission AC voltage wave, transmitted over a low voltage power distribution line and a leased line.
2. The Prior Art
The conventional transmission system using a power distribution line as shown in FIG. 5, has superimposed, as shown in FIG. 5, only the data transmission signals D.sub.o .about.D.sub.n for every several cycles to several tens of cycles of the commercial frequency voltage 1 (for example, Japanese Patent Laid-Open No. 58-12291). In the former case, since the level and phase of data transmission signals D.sub.o .about.D.sub.n change due to the load fluctuation of the power distribution lines, these signals are not stable when finally received. Therefore, in the latter case, the data transmission signals D.sub.o .about.D.sub.n are monitored by comparing the reference transmission signal R received in the receiving side with the following data transmission signals D.sub.o .about.D.sub.n, but it has been difficult to ensure highly reliable communication due to the change in level and phase of data transmission signals D.sub.o .about.D.sub.n in every cycle of commercial frequency voltage 1.